1. Field of the Invention
The present invention relates to a plate-link chain, in particular for a motor vehicle drive system, with a large number of link plates pivotally connected with each other by rocker members that extend transversely to the longitudinal direction of the plate-link chain and are positioned in openings of the link plates.
2. Description of the Related Art
Such chains having link plates and rocker members include curved contact surfaces located on each of the rocker members and on the link plates. The rocker members and link plates bear against each other at the contact surfaces to transmit power. The contact surfaces are provided on upper and lower contact surface areas of the rocker members in the rocker member height direction. Curved rolling surfaces are situated on the rocker members, along which surfaces the rocker members roll against each other to transmit power. In a cross section running in the longitudinal direction of the plate-link chain through a center of mass of the rocker member, the rolling surfaces extend into an upper area above the plane of the cross section and into a lower area below it.
Such a plate-link chain installed in a belt-driven conical-pulley transmission, for example, is also referred to as a rocker member chain. The rocker members, or pressure members, arranged in pairs in plate openings of the link plates, have rolling surfaces with which they roll against each other. In so doing the rocker members receive the tractive force transmitted by the plate-link chain in the form of compressive stresses, and as the reactive force thereto they introduce corresponding forces into the link plates, wherein the transfer of force between the rocker members and the link plates takes place at curved contact surfaces that are formed on the rocker members and on the link plates.
If the plate-link chain is circulating in a belt-driven conical-pulley transmission, as it runs onto a conical disk pair the plate-link chain passes from an extended position into a curved position, and the link plates are subjected to different tensile force loads at their so-called upper strap and lower strap. As the plate-link chain runs through a complete circulation, those tensile forces have steeply rising peak loads that increase the load on the plate material and thus have a negative effect on the service life of the plate-link chain or on its torque transmitting capacity.
Since the pressure forces transmitted between the individual rocker members at the rolling surface are introduced into the link plates, from the pressure forces in the area of the contact surfaces corresponding pressure force transmissions occur here with resulting high surface pressures. If the surface pressures become too high, creep can occur in the area of the contact surfaces, accompanied, in turn, by a limitation of the service life or a limiting of the torque transmitting capacity.
The rocker members bear against each other at their curved rolling surfaces, and they function as a joint. Thus, during a rolling against motion as the chain circulates around two conical pulleys that are spaced from each other, the rolling point between the rolling surfaces of opposing rocker members, seen in a cross sectional view perpendicular to the running direction of the plate-link chain, undergoes a displacement between an upper area above and a lower area below a virtual cross-section plane running through the center of mass in the longitudinal direction of the plate-link chain.
In the case of rocker members of known plate-link chains, the rolling surface so defined lies symmetrically above and below the center of mass of the rocker member. That means, in other words, that the length of the rolling surface in known rocker members, viewed in the direction of rocker member height, extends symmetrically to a cross section plane running through the center of mass in the running direction of the plate-link chain. That form of the rolling surface was made in the case of known plate-line chains on the assumption that a corresponding symmetrical load and thus symmetrical distribution of force on the link plates in the area of the upper and lower contact surfaces is achieved thereby.
But it has now been found that that form of the rolling surfaces on the rocker members, largely symmetrical to the center of mass of the rocker members, results in a significantly more non-uniform surface pressure load on the contact surfaces of the link plates in the upper and lower contact surface areas. Thus, the pressures in the lower contact surfaces, i.e., the transition area of the lower strap of the link plates, close to the axis, are significantly higher than the surface pressures in the upper contact surface area, i.e., in the area between the contact surfaces of the rocker members and the contact surfaces of the upper strap of the link plates.
An object of the present invention is to refine the plate-link chain in such a way that the pressure loading between the lower and upper contact surfaces of the link plates is more uniform, and thus the service life of the plate-link chain can be prolonged, or the torque transmitting capacity of the plate-link chain can be increased.